Vertically movable workpiece support device

Abstract

A vertically movable workpiece support device has a ratchet wheel with a larger diameter than the outer diameter of a driving sprocket wheel and is concentrically attached to an end surface of a boss portion in the driving sprocket wheel. A pair of left and right bearing members are provided side by side, on a side on which the free end side of a drive chain is horizontally extended with respect to the driving sprocket wheel, so as to sandwich a horizontally extending path section of the drive chain. A movable pawl is pivotally supported between the pair of left and right bearing members and engages with the ratchet wheel to block the rotation of the ratchet wheel caused by the movement of the drive chain when the workpiece support base is lowered. An actuator switches the movable pawl to a non-action position with respect to the ratchet wheel.

What is claimed is: 
     
       1. A vertically movable workpiece support device, comprising:
 a raising/lowering drive means that drives a workpiece support base supported so as to be parallelly and vertically movable to raise and lower the workpiece support base; 
 the raising/lowering drive means having a drive chain that is bendable to only one side and a driving sprocket wheel driven by a motor that engages with the drive chain, in which the drive chain supports the workpiece support base in a vertically linear path section, where the drive chain is extended from one end portion coupled to the workpiece support base to a portion engaging with the driving sprocket wheel and in which a part of the drive chain on a free end side from the driving sprocket wheel is extended horizontally through a lower side of the driving sprocket wheel; 
 a ratchet wheel having a larger diameter than an outer diameter of the driving sprocket wheel is concentrically attached to an outer side of the driving sprocket wheel, a pair of left and right bearing members are provided side by side, on a side on which the free end side of the drive chain is horizontally extended with respect to the driving sprocket wheel, so as to sandwich a horizontally extending path section of the drive chain; 
 a movable pawl which engages with the ratchet wheel so as to block rotation of the ratchet wheel caused by a movement of the drive chain when the workpiece support base is lowered is pivotally supported between the pair of left and right bearing members; 
 an actuator operable to switch the movable pawl to a non-action position with respect to the ratchet wheel; 
 an upper end portion of the movable pawl is pivotally supported at a height of a circumferential edge of the ratchet wheel, an expanded part of the movable pawl between the upper end portion and a lower end pawl portion is expanded to a side away from the ratchet wheel, and gravity acting on the expanded part causes a rotation force on the movable pawl in such a direction that the lower end pawl portion biased toward and engages with a circumferential edge of the ratchet wheel; 
 the expanded part of the movable pawl has a notched concave portion having a rear side and lower side which are open on a side opposite to the ratchet wheel, engagement holes are provided in both left and right side wall portions of the notched concave portion, a tip end of a drawing-in shaft of the actuator is disposed in the concave portion, a tip end of a drawing-in shaft of the actuator is disposed in the notched concave portion, and both end portions of a drive pin attached to the tip end of the drawing-in shaft are fitted into the engagement holes, and 
 each engagement hole has a shape and size to allow certain movement of the drive pin therein such that an engagement/disengagement swing movement of the movable pawl caused by the rotation of the ratchet wheel when the workpiece support base is raised is not transmitted to the drive in, and when the drawing-in shaft of the actuator is made to perform a drawing-in operation, the movable pawl is held in a state where the movable pawl is disengaged from the ratchet wheel via the dove pin and the engagement holes. 
 
     
     
       2. The vertically movable workpiece support device according to  claim 1 , further comprising:
 the ratchet wheel having a number of pawls each having a height; 
 a second ratchet eel made of a resin is rotated integrally and concentrically with the ratchet wheel, and the second ratchet wheel has the same number of pawls as the ratchet wheel; and 
 the second ratchet wheel having pawls which are taller in height than the pawls of the ratchet wheel such that an engagement of the movable pawl between the pawls of the ratchet wheel is allowed but that when the movable pawl rides over the pawls of the ratchet wheel, the movable pawl is floated up from the pawls of the ratchet wheel.